A common method of coloring plastics is to use color concentrate pellets. A color concentrate pellet is solid and is typically comprised of pigment and carrier. The pigment colors the plastic. The carrier acts as a binder and generally also acts to “wet” the pigment so that the pigment will mix well with the resin or plastic to be colored and so that the pigment will be well dispersed throughout the final molded, extruded, cast, or otherwise formed plastic product.
In conventional color concentrate pellets, the pigment is mixed with a carrier which is a thermoplastic resin material such as polypropylene, polyethylene, ABS, or polystyrene. The materials and the pellets produced thereby have a melting point in the range of 300° F. to 550° F. To make conventional color concentrate pellets, the pigment and carrier are mixed and heated to about 400° to 600° F. The mixture melts and is mixed, and is extruded through an extruder and then solidifies and is cut into conventional pellet size.
These conventional color concentrate pellets contain organic and inorganic pigments, and are typically 30% to 50% pigment by weight with the balance being thermoplastic resin.
These conventional pellets are then mixed with natural resin pellets of the same general size and shape to effect colorization. Natural resin pellets are pellets which have not yet been colored. Commercially sized natural resin pellets include those that are cylindrically shaped and/or round shaped, are about ⅛ inch in diameter, and are about ⅛ to ¼ inch long or approximately ⅛″ round. Other commercially sized natural resin pellets, individually, have similar bulk or volume, but may have other regular geometric shapes or may have somewhat irregular shapes.
One problem with conventional color concentrate pellets is that the carrier generally must be compatible with the natural resin to be colored. To be compatible, the two must be the same or very similar. For example, a polypropylene carrier would be compatible with a polypropylene natural resin, but would not be compatible with PVC natural resin. Mixing a carrier with an incompatible natural resin could adversely affect the physical properties of the final molded product. The typical end product would comprise 96% natural resin, 2% carrier, and 2% pigment.
Another problem is that the high temperatures utilized in the extrusion process (400° F.-600° F.) tend to burn out or degrade organic pigments and certain inexpensive inorganic pigments which burn out or degrade between 400° F. and 550° F.
The conventional process is particularly disadvantageous with regard to organic pigments. Organic pigments tend to be more heat-sensitive, more unstable, and generally more expensive than inorganic pigments. The high temperatures of the conventional process are bad for organic pigments. The high temperatures also tend to use up a significant portion of the available heat history or heat tolerance of the pigments and carriers utilized. These high temperatures are thus disadvantageous.
Another known highly loaded concentrate pellet and a related process are disclosed in U.S. Pat. No. 7,442,742 to Smink et al., the entire disclosure of which is hereby incorporated herein by reference. Smink et al. describes a highly loaded concentrate pellet composition comprising a colorant, a thermoplastic carrier, and a metallocene polymer processing aid. The metallocene polymer processing aid is a substantially amorphous metallocene polypropylene polymer or copolymer. In particular, the concentration of colorant in Smink et al. is about 15-75% by weight, the thermoplastic carrier is about 9-60% by weight, and the metallocene polymer is about 2-20% by weight.
There is a continuing need for a highly loaded concentrate pellet having a carrier that is compatible with a wide range of natural resins, which can comprise up to 93% active ingredient, with a carrier which will melt at less than about 290° F., for better mixing, and will be manufactured at temperatures of less than 300° F., so as not to burn out or degrade certain heat-sensitive pigments, particularly organic pigments, which have heat sensitivity in the range of 400° F. to 550° F. Desirably, the highly loaded concentrate pellet, will not settle out upon mixing with commercially sized natural resin pellets, will look comparable to a conventional color concentrate pellet, can be made with less energy cost, and can be processed to pellet form at less than 290° F. and not unduly heat or otherwise adversely affect the qualities of organic pigments.